1. Introduction to Chemical Vitiligo 

Chemical vitiligo is an underdiagnosed condition that falls within the broader category of vitiligo disorders. It typically manifests as depigmentation of the skin following repeated exposure to certain chemicals. Unlike common vitiligo, chemical vitiligo generally has a better prognosis and is relatively easier to treat. Many patients experience gradual improvement after a period of treatment (such as phototherapy) without further chemical exposure. Consequently, a small number of patients may exhibit spontaneous remission or "self-healing" of white spots, although this phenomenon lacks universal applicability.

For diagnosed vitiligo patients, it is crucial not to underestimate the significance of chemical vitiligo. Chemical exposure can act as a catalyst, exacerbating immune dysregulation and potentially leading to the worsening of vitiligo. Chemical vitiligo represents a distinct form of vitiligo development, with chemical exposure being a potential trigger for its onset and progression. 

2. Pathogenesis of Chemical Vitiligo

The development of chemical vitiligo is closely linked to chemical exposure. Many patients mistakenly attribute it to an "allergic reaction," assuming that only the exposed areas will develop white spots. However, studies have shown that lesions can appear not only at the site of contact but also on distant skin regions. Approximately 26% of chemical vitiligo cases exhibit lesions that spread beyond the initial exposure site.

This phenomenon occurs because chemical vitiligo involves both chemical stimulation and immune responses. The primary culprits are phenols and catechol derivatives, which structurally resemble tyrosine. These compounds preempt the catalytic center of tyrosinase, blocking melanin synthesis and promoting the continuous production of free radicals and exosome secretion. Excessive free radicals disrupt the body's oxidative-antioxidant balance, triggering oxidative stress and inflammatory reactions, ultimately leading to melanocyte death and skin depigmentation. Exosomes act as messengers, delivering new antigens to neighboring immune cells, activating autoreactive T cells and cytotoxic melanocytes, thereby contributing to the progression of vitiligo.

3. Identification of Chemical Vitiligo

Common vitiligo initially presents as one or several hypochromic spots with unclear boundaries, gradually expanding into well-defined milky white patches. In contrast, chemical vitiligo often begins with mottled multiple spots, affecting individuals ranging from 78 days to 84 years old, predominantly adults. Lesions are commonly found in areas directly exposed to chemicals, such as hands, wrists, and forearms, though some may appear far from the contact site.

4. Prevention of Chemical Vitiligo

Clinical management emphasizes prevention over treatment. Studies indicate that 70.7% of chemical vitiligo cases result from household chemical exposure. Avoiding certain chemicals in daily life is key to preventing the onset and spread of chemical vitiligo. Notable risk factors include hair dyes, disinfectants, detergents, and rubber products.

- Hair Dye: A large prospective study reported a 50% higher risk of developing vitiligo among women who started using hair dye before age 30 or used it for more than five years. Phenols and phenylenediamines in hair dyes are particularly harmful to melanocytes, potentially causing local immune imbalance, hair loss, skin allergies, and vitiligo progression.

- Disinfectants and Detergents: Phenol derivatives, commonly found in these products, hinder melanin synthesis. Long-term exposure increases the risk of vitiligo development.

- Rubber Products: Antioxidants like quinone monobenzyl ether, used in rubber processing, can damage skin upon prolonged contact, leading to white spots. This damage can spread via neuroimmune mechanisms, exacerbating vitiligo.

Given the ubiquity of chemicals in daily life, minimizing contact with irritants is essential. If you observe abnormal white spots, especially post-chemical exposure, discontinue contact immediately and seek medical advice.